Association between premenopausal progestogen use and postmenopausal hormonal therapy in the GAZEL cohort

Physician characteristics play an important role in the use of progestogens before menopause. Our results also suggest that women using progestogens may have a higher risk of breast cancer, that is, that progestogen use may be a confounding rather than causal factor. The analyses concerning the relationship between EPT use and breast cancer risk must take progestogen use before menopause into account, as they do other confounding factors, such as age at menarche, parity, and use of oral contraceptives.